This invention relates to powder actuated tools, and more particularly to a powder actuated tool having an improved muffler arrangement to reduce the noise level of the tool. The operation of the powder actuated tools is accompanied by a certain level of noise due to the ingnition of the propellant charge and the expansion of gases generated thereby. In certain applications, some noise may be objectionable due to excess surrounding noise. One such application is the use of a powder-actuated tool in steel mills to fasten heat insulating boards to the inside of the upper end of an ingot mold to provide heat insulating liners or "hot top". Because of the noise level normally present in the steel mill, the additional noise due to the operation of a powder actuated tool may be considered objectionable.